In typical combined cycle power generation systems, cooling of gas turbine high temperature components and the accompanying steam cycle are usually of the following types:
(1) Air Cooled Gas Turbine--The gas turbine high temperature components are cooled by air extracted or conducted from other components in the gas turbine cycle. The steam cycle and the gas turbine coolant streams are not integrated.
(2) Water Cooled Gas Turbine--The gas turbine high temperature components are cooled with water in the liquid phase. The heat extracted from the high temperature gas turbine components is integrated with the combined cycle steam bottoming cycle. The energy extracted from the high temperature section of the gas turbine is transported to the low temperature portion of the steam cycle to maintain the water in the liquid phase, thus compromising thermal efficiency of the cycle.
(3) Steam Cooled Gas Turbine Integrated Into a Combined Cycle with Multiple Pressure--This cycle uses steam from the low pressure section of a multiple pressure combined cycle heat recovery steam generator (HRSG) to cool the high temperature components of the gas turbine with energy extracted from the gas turbine returned to the low pressure section of the steam cycle. This system is described in U.S. Pat. No. 4,424,668.
In combined cycle systems, as disclosed in parent application Ser. No. 08/161,070, superheated steam temperature leaving the HRSG is controlled (and cooled) by injection of a water spray in a conventional steam attemperator located upstream of the final superheater passes. The water source is typically a high pressure feed water pump located upstream of the HRSG economizer. It has been found, however, that contamination of the HRSG superheater and ultimately the gas turbine and/or steam turbine itself could result by reason of the introduction of unpurified water into the attemperator.